Essentially, it is known that a thermal magnetic circuit breaker is a manually or automatically operating electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit, for example. Its basic function is the detection of a fault condition and the interruption of current flow. Therefore, the thermal magnetic circuit breaker has for example at least one magnetic trip device in order to prevent the electrical circuit or an electrical device from damage by short circuit and a thermal trip device in order to prevent the electric circuit or an electrical device, like a load, from damage by overload. A short circuit is an abnormal connection between two nodes of the electric circuit intended to be at different voltages. This results in an excessive electric current, named an overcurrent limited only by the Thévenin equivalent resistance of the rest of the network and potentially causes circuit damage, overheating, fire or explosion. An overload is a less extreme condition but a longer-term over-current condition as a short circuit.
The thermal magnetic circuit breaker or breaker, respectively, has different settings or adjustments, respectively, as to where does the client wants the breaker to trip thermally. These settings go from 0.7 ln to 1 ln, wherein 0.7 ln means 70% of the nominal current rated on the breaker and 1 ln means 100% of the nominal current rated on the breaker. Therefore, in a 140 Amp breaker, 70% will be 700 Amp. Basing on a lower thermal adjustment, less electrical current goes through a conductive element like a conductor and results on a lower temperature on a bimetal element of the thermal trip device. Thus, the temperature profile of the thermal trip device of the thermal magnetic circuit breaker or thermal magnetic trip unit (TMTU) presents low temperature behaviour on the lower thermal adjustment side, which is for example 70% ln and therefore 70% of the nominal current, as mentioned above. Since the movement of the bimetal element is a result of the temperature, such a low temperature is not enough in order to reach deflection and force of the bimetal element of the thermal trip device, which are necessary to unlatch the breaker mechanism. Therefore, a lower electrical current inducts a less temperature and as a consequence a less deflection and/or force of the bimetal element, during a high electrical current inducts a higher temperature and as a consequence a higher deflection and/or force of the bimetal element.